Question

我想在main select语句中使用city列的前缀（即：l.city），就像在内部select子查询语句中一样，以获得更“理解”和更好看的方式可以这么说但是我不能，因为它给了我ORA-00904：“L”。“城市”：标识符无效，仅使用没有标识符的城市，为什么？这是代码：

   SELECT d.department_name, l.city
   FROM  departments d
   NATURAL JOIN (SELECT l.location_id,l.city,l.country_id
                  FROM       locations l
                  INNER JOIN countries c
                  ON (l.country_id = c.country_id)
                  INNER JOIN regions r
                  ON (c.region_id = r.region_id)
                  WHERE r.region_name = 'Europe');

Answer 1

您的"L"别名位于视图中，因此在您要使用它的位置不可见。

试试这个：

   SELECT d.department_name, x.city
   FROM  departments d
   NATURAL JOIN (SELECT l.location_id,l.city,l.country_id
                  FROM       locations l // <-- "l" has no scope outside brackets
                  INNER JOIN countries c
                  ON (l.country_id = c.country_id)
                  INNER JOIN regions r
                  ON (c.region_id = r.region_id)
                  WHERE r.region_name = 'Europe') x;

Answer 2

只需为子查询添加别名，或删除l.中的l.city：

SELECT d.department_name, l.city
FROM  departments d NATURAL JOIN
      (SELECT l.location_id,l.city,l.country_id
       FROM locations l INNER JOIN
            countries c
            ON (l.country_id = c.country_id) INNER JOIN
            regions r
            ON (c.region_id = r.region_id)
       WHERE r.region_name = 'Europe'
      ) l

Answer 3

你需要定义＆＃39; l＆＃39;主查询中的别名。

SELECT d.department_name, subl.city
FROM  departments d
NATURAL JOIN (SELECT l.location_id,l.city,l.country_id
              FROM locations l
              INNER JOIN countries c ON l.country_id = c.country_id
              INNER JOIN regions r ON c.region_id = r.region_id
              WHERE r.region_name = 'Europe') subl;

ORA-00904：在from子句中使用自然连接并与子查询中的内部连接结合使用时，标识符无效

3 个答案: